Copper-Nickel Alloys - Cupronickel (UNS C70600 - C71500)– Wrought Alloys

Topics Covered

Introduction

Cu-Ni alloys have a single-phase structure throughout the complete range of compositions and many standard alloys are available with small variations in their element composition for special applications. The earliest application of Cu-Ni alloy was for marine condenser tubes and presently it has many uses. Apart from their usage in coinage and wire mesh, Cu-Ni alloys containing 10 to 30% nickel with iron and manganese additions (C70600 and C71500) are also used for marine applications.

Alloying Additions

Manganese in commercial alloys acts as a de-sulfurizer and de-oxidant. It enhances the working characteristics and anti-corrosiveness in sea-water.

Chromium can also be added instead of iron to increase strength. It is usually added in a 30% nickel casting alloy.

Iron is supplemented (up to about 2%) to the alloys used in marine applications, as it improves the alloy’s strength and provides better resistance to corrosion caused by flowing seawater. Optimum compositions of the copper-nickel-iron alloys offer resistance to corrosion for materials used in making tubes, condensers and other applications which require contact in sea-water. The term "copper-nickel (Cu-Ni)" refers to copper-nickel-iron alloys.

Silicon increases the casting ability of Cu-Ni alloys and is used in combination with either chromium or niobium.

Niobium, when added to cast versions of 10% and 30% nickel alloys, acts as a hardening element. It makes the welding of cast alloys easy.

Addition of tin offers improved resistance to atmospheric tarnishing. The alloy C72500 comprises 2% tin and 9% nickel.

Classification

¹Cu + Sum of named elements, 99.5% min.
²Ni value includes Co.
³Ag Includes B
⁴Includes Co
⁵The following additional maximum limits shall apply: .02% C, .015% Si, .003% S, .002% Al, .001% P, .0005%Hg, .001% Ti, .001% Sb, .001% As, .001% Bi, .05% Co, .10% Mg and .005% Oxygen. For C70690, Co shall be .02% max.
⁶The following additional maximum limits shall apply: .07% C, .15% Si, .024% S, .05% Al and .03% P.
⁷.02% P, max.; .25% Si, max.; .01% S, max.; .02 - .50% Ti.
⁸The following additional maximum limits shall apply: When the product is for subsequent welding applications and is so specified by the purchaser, .50% Zn, .02% P, .02% Pb, .02%S and .05% C.
⁹Cu + Sum of named elements, 99.8% min.
¹⁰Cu + Sum of named elements, 99.7% min.
¹¹.005% Pb, max., for hot rolling.
¹²Includes Co